In recent years, advances in electronic devices have resulted in a demand for compact and lightweight heat sinks particularly excelling in heat dissipation, for which heat sinks must be made thinner and in complicated shapes. On the other hand, aluminum alloys generally have a higher thermal conductivity with a higher aluminum purity level. Hence, when requiring high thermal conductivity, one might contemplate using pure aluminum, but pure aluminum has poor strength and is difficult to cast, so it has not been possible to cast any in complicated shapes or having thin portions.
Thus, when producing a heat sink having a complicated shape or a thin portion, such as described in JP 2001-316748A, JP 2002-3972A or JP 2002-105571A, an aluminum alloy containing Si is used to improve the castability even at the cost of sacrificing some of the thermal conductivity.
While these conventional alloys are alloys having Si and Fe added to aluminum, the content of elements such as Cu, Mn, Zn and Mg that are normally contained in aluminum alloys is limited in order to prevent the thermal conductivity of the alloys from decreasing. As a consequence, the strength of the alloys can be inadequate, so that the cast articles can deform or break when separating them from the mold after casting, thus resulting in low productivity. Additionally, the poor strength causes burrs to easily form during post-processing such as cutting, and screw holes and the like can have inadequate strength. Furthermore, since the use of scrap is restricted and the raw material of the alloy ingots is limited, the alloys perform poorly in economic terms and in environmental terms especially in view of recycling, as compared with common die casting materials such as alloy JIS-ADC12.
In order to solve the above-indicated problem relating to the strength of the alloy material, the alloy materials described in JP 2005-298856A and JP 2006-63420A have been proposed.
These conventional alloy materials are alloy materials obtained by subjecting an alloy composed of aluminum with Si and Fe, with Mg further added, to a heat treatment, and they are capable of improving the strength without greatly reducing the thermal conductivity of the alloy material, by restricting the content of elements such as Cu, Mn and Zn that are usually contained in aluminum alloys. Therefore, they perform poorly in economic terms and in environmental terms especially in view of recycling, as mentioned above. Additionally, they cannot easily share melt furnaces with common die casting materials such as alloy JIS-ADC12, and therefore must be provided with special melting and casting equipment.
Patent Document 1: JP 2001-316748A
Patent Document 2: JP 2002-3972A
Patent Document 3: JP 2002-105571A
Patent Document 4: JP 2005-298856A
Patent Document 5: JP 2006-63420A